Doesn't it just mean that Locke hadn't time travelled yet? Alpert was just checking, i think we are supposed to assume that Locke knew the right answer but hid it from Alpert.... why would he want to do that??? Oh by the way: I agree, Richard Alpert is fantastically gorgeous- i tingle all over when he appears!
Why is he the only one of the Others who travels through time (that MUST be what he's doing surely!??) I used to think he's ageless (like Jacob?) but not so sure now.
